Low-energy excitations and dynamic Dzyaloshinskii-Moriya interaction in αNaV2O5 studied by far-infrared spectroscopy

T. Rõõm, D. Hüvonen, U. Nagel, Y.-J. Wang, and R. K. Kremer
Phys. Rev. B 69, 144410 – Published 8 April 2004
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Abstract

We have studied far-infrared transmission spectra of αNaV2O5 between 3 and 200cm1 in polarizations of incident light parallel to a, b, and c crystallographic axes in magnetic fields up to 33 T. The temperature dependence of the transmission spectra was studied close to and below the phase-transition temperature Tc=34K. The triplet origin of an excitation at 65.4cm1 (8.13 meV) is revealed by splitting in the magnetic field. The g factors for the triplet state are ga=1.96±0.02, gb=1.975±0.004, and gc=1.90±0.03. The magnitude of the spin gap at low temperatures is found to be magnetic-field independent at least up to 33 T. All other infrared-active transitions appearing below Tc are ascribed to zone-folded phonons. Two different dynamic Dzyaloshinskii-Moriya (DM) mechanisms have been discovered that contribute to the oscillator strength of the otherwise forbidden singlet to triplet transition. First, the strongest singlet to triplet transition is an electric dipole transition where the polarization of the incident light’s electric field is parallel to the ladder rungs (E1a). This electric dipole active transition is allowed by the dynamic DM interaction created by a high-frequency optical a-axis phonon. Second, in the incident light polarization perpendicular to the ladder planes (E1c) an enhancement of the singlet to triplet transition is observed when the applied magnetic field shifts the singlet to triplet resonance frequency to match the 68cm1 c-axis phonon energy. The origin of the second mechanism is the dynamic DM interaction created by the 68cm1 c-axis optical phonon. The strength of the dynamic DM is calculated for both mechanisms using the presented theory.

  • Received 1 December 2003

DOI:https://doi.org/10.1103/PhysRevB.69.144410

©2004 American Physical Society

Authors & Affiliations

T. Rõõm*, D. Hüvonen, and U. Nagel

  • National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia

Y.-J. Wang

  • National High Magnetic Field Laboratory, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, Florida 32306, USA

R. K. Kremer

  • Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart, Germany

  • *Electronic address: roomtom@kbfi.ee

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Issue

Vol. 69, Iss. 14 — 1 April 2004

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